This invention relates to a method for the manufacture of novel perfluorotetrahydrofuran derivatives represented by the following generic formula. ##STR1## (WHEREIN, R.sub.f.sup.1 stands for a fluorine atom or a straight-chain aliphatic perfluoroalkyl group having 1 to 7 carbon atoms and R.sub.f.sup.2 for a straight-chain aliphatic perfluoroalkyl group having 1 to 7 carbon atoms).
The compounds represented by the formula (1) are colorless, transparent, odorless liquids having extremely high thermal and chemical stability and are usable as solvents, solution media, etc. Heretofore, cyclic fluorinated ethers have been manufactured by various methods such as electrolytic fluorination of cyclic ethers (U.S. Pat. No. 2,594,272 and British Pat. No. 672,720), electrolytic fluorination of straight-chain carboxylic acids and derivatives thereof (U.S. Pat. No. 2,644,823, British Pat. No. 718,318, German Pat. No. 1,069,639 and French Pat. No. 1,636,296), electrolytic fluorination of alcohols (Japanese Patent Public Disclosure No. 123658/1975), electrolytic fluorination of aldehydes (Japanese Patent Publication No. 4,994/1976), etc. None of these methods relate in any way to such perfluoro-(2,4-dialkyltetrahydrofuran)s as are represented by the formula of (1) given above. Although German Pat. No. 1,069,639 is similar in some respects to the invention of this patent application in terms of raw material, product and method, it is different from this invention in that it necessitates use of an electric conduction agent and in other respects.
Heretofore, perfluoro-(2,4-dialkyltetrahydrofuran)s have been manufactured such as by electrolytic fluorination of monoalcohols having a side-chain group at the .alpha. position (represented by RCH.sub.2 OH, wherein R stands for a saturated or unsaturated, straight-chain or side-chain aliphatic alkyl group having 3 to 9 carbon atoms) (Japanese Patent Public Disclosure No. 88062/1975).
This method, however, has entailed a disadvantage that the electrolytic fluorination by-produces a large amount of a fluorocarbon having the same number of carbon atoms as the alcohol being used as the raw material and the separation of this by-product from the perfluoro-cyclic ether is difficult to carry out.
The inventors, in search of a method capable of producing perfluoro-(2,4-dialkyltetrahydrofuran)s of the aforementioned formula (1) by electrolytic fluorination, made an elaborate study of electrolytic fluorination of carboxylic acids and derivatives thereof. They have consequently made a discovery that the compounds of the aforementioned formula (1) are obtained in high yields by electrolytically fluorinating, under the conditions described hereinafter, carboxylic acids having side-chain groups particularly at the .alpha. position and derivatives thereof. They have accomplished this invention on the basis of this discovery.
An object of the present invention is to provide a method for the manufacture of perfluoro-(2,4-dialkyltetrahydrofuran)s by electrolytic fluorination.